Sweep improvement by use of static blocks between injection and production wells to influence the interface of the driving fluid



O United States Patent [111 3,537,527

[72] Inventor George M. Wood 3,109,487 11/1963 Hoyt 166/245 Houston, Texas 3,113,617 12/1963 Oakes..... 166/245 [21] Appl. No. 811,086 3,205,943 9/1965 Foulks.... 166/245 [22] Filed March 27, 1969 3,215,198 11/1965 Willman 166/263 Continuation-impart of application Ser. No. 3,256,933 6/1966 Murphree et al.. 166/274X 786,566, Dec. 24, 1968, now pending 3,288,212 1 1/1966 OBrian et al 166/274X [45] Patented Nov. 3, 1970 3,402,768 9/1968 Felsenthal etal 166/245 1 Assisnee Texmlnc, OTHER REFERENCES New Muskat, Physical Principles of Oil Production, First Edition, M McGraw-Hill Book Company Inc., New York, 1949, pp. 670

541 SWEEP IMPROVEMENT BY USE OF STATIC Primary Emminer$IPhen J Novosad L K BETW EN INJECTION N A ttomey- K. E. Kavanagh and Thomas H. Whaley PRODUCTION WELLS T0 INFLUENCE THE INTERFACE OF THE DRIVING FLUID 18 m 18 Drawing Figs. ABSTRACT: A barrier comprising a slug of a fluid more [52] U.S.Cl 166/245, viscous than f ti hydrocarbons is injected via a we 66/274 between the injection and production wells to retard the for- [51] Int. Cl E2lb 43/16, mation f the usual cusp at the interface between the injected 43/20 driving and the formation fluids as it advances toward a [50] Field of Search 166/245, production we AS applied specificany to thirteen and seven, 263 teen well patterns, this barrier can be placed strategically via the side wells of these atterns to affect the flow of drivin [56] References Cited fluid to result in a more complete sweep of the formatioi t UNITED STATES PATENTS fluids, as production wells are changed to function as injection 3,074,481 1/ 1963 Habermann 166/274X wells at predetermined periods.

Patented Nov. 3, 1970 Sheet Patented Nov. 3, 1970 Sheet 2 of 3 0 Jo P a 06 is a s pmv o m E. A VA 0 J4 a X s s w C k x P n \m k\ 5 y 1 M\ Q m K p #5 P m 7D 0 d) B a k p m ,p I m p; W A, fiv am PM, Ll. PC m k j. a 0 4. W S 1 z A T w A 0 1202 was Bill SWEEP IMPROVEMENT BY USE OF STATIC BLOCKS BETWEEN INJECTION AND PRODUCTION WELLS TO lNFLUENCE THE INTERFACE OF THE DRIVKNG FLUlD CROSS REFERENCE This is a continuation-in-part application for patent of my copending application for patent for Sweep improvement By Use Of A Static Block Between lnjection and Production Wells To Delay Cusp Formation, Ser. No. 786,566, filed Dec. 24, 1968.

FlELD OF THE INVENTION This invention relates generally to the production of hydrocarbons from underground hydrocarbon-bearing formations, and more particularly, to a method for increasing the efficiency of the production of hydrocarbons therefrom.

DESCRlPTlON OF THE PRiOR ART in the production of hydrocarbons from permeable underground hydrocarbon-bearing formations, it is customary to drill one or more boreholes or wells into the hydrocarbonbearing formation and produce hydrocarbons, such as oil, through designated production wells, either by the natural formation pressure or by pumping the wells. Sooner or later, the flow of hydrocarbons diminishes and/or ceases, even though substantial quantities of hydrocarbons are still present in the underground formations.

Thus, secondary recovery programs are now an essential part of the overall planning for virtually every oil and gas-condensate reservoir in underground hydrocarbon-bearing formations. In general, this involves injecting an extraneous fluid, such as water or gas, into the reservoir zone to drive formation fluids including hydrocarbons toward production wells by the process frequently referred to as flooding. Usually, this flooding is accomplished by injecting through wells drilled in a geometric pattern, the most common pattern being the fivespot.

When the driving fluid from the injection well reaches the production wells of a five-spot pattern, the areal sweep is about 7! percent. By continuing production considerably past breakthrough, it is possible to produce much of the remaining unswept portion. It would be a great economic benefit to be able to achieve a sweep of I percent of the hydrocarbom bearing formation. It would be an even greater benefit to be able to achieve it at breakthrough, so that it would not be necessary to produce large quantities of injected driving fluid.

It is understood that the failure of the driving flood in secondary recovery operations to contact or sweep all the hydrocarbon zone is due to the development of a cusp, at the interface between the driving and the driven fluids, which advances toward the production well. If other portions of the interface could be made to keep up, or if the cusp formation were delayed, e.g. by a block, a more complete zonal sweep would be possible. In the commonly assigned US. Pat. No. 3,393,735, issued to A. F. Altamira et al. on July 23, 1968 for interface Advance Control in Pattern Floods by Use of Control Wells, there is disclosed how an increased amount of hydrocarbons is produced and recovered from an underground hydrocarbon-bearing formation by employing at least three wells, penetrating such a formation, which wells are in line, to produce hydrocarbons from the formation via two of these wells including the middle well, as disclosed in the commonly assigned U.S. Pat-No. 3,109,487, issued to Donald L. Hoyt on Nov. 5, 1963 for Petroleum Production by Secondary Recovery. In both these cited patents, there is disclosed how a production control well is positioned between the injection well and the production well and is kept on production after the injection fluid reaches it. In this manner, the cusp is pinned down at the control well, and while the zone swept out by the injection fluid before breakthrough at the outer production well is increased, there is an unwanted handling of considerable quantities of injection fluid at the control well.

Another aspect to increase the sweep is disclosed in the commonly assigned U.S. Pat. No. 3,393,734, issued to D. L. l-loyt et al. on July 23, 1968 and involves the retardation of the development of the cusp toward a production well. The method of achieving more uniform advance is to control the flow gradients so that the interface is spread out. This can be done either by choosing a particular geometry of well positions or by adjusting the relative production rates so that the velocity of advance is not predominantly in one direction. lt can be done also by shifting the gradients frequently, in both direction and magnitude, thus preventing any one portion of an interface from advancing too far out of line.

SUMMARY OF THE INVENTION lt is an overall object of the present invention to provide an improved secondary recovery procedure involving initially three wells in line as part of a well arrangement for exploiting a hydrocarbon-bearing formation, by changing the How pattern ofthe injected extraneous driving fluid, using for this pur pose, strategically placed fluids having higher viscosity than the reservoir hydrocarbons and the extraneous driving fluid. The function of some of the wells in the arrangement may be changed at strategic times to gain maximum control of the interface or flood front.

A three well group is arranged in line so that an end well is completed for production and the remaining two wells are offset with the outer well thereof being completed for injection. Secondary recovery by flooding may be initiated by injection of a highly viscous fluid via the inner of the offset wells with production from the end (outer) production well until such time as a sufficient volume ofthe highly viscous fluid has been injected to form a viscous bubble of desired size. Then the inner of the offset injection wells is shut in and injection of an extraneous driving fluid, such as water, is initiated at the outer injection well. The injected driving fluid is forced to travel a longer path around the viscous barrier and the formation ofa cusp is blocked.

Flooding also may be initiated by simultaneous injection into the two offset wells, with the highly viscous fluid being put into the inner of these two wells, and the lower viscosity driving fluid being injected into the outer of the two offset wells, with the inner of the two wells being shut in after the desired volume of highly viscous fluid has been injected into the formation.

The flood can be initiated by injection of the extraneous driving fluid in the outer offset well and the placement of the viscous bubble could be delayed to any time until the interface reached the inner offset well, in which case the inner offset well could be used as a production well until interface breakthrough thereat, and then converted to an injection well for the placement of the viscous bubble. The well could be used to produce past breakthrough and pin the cusp until a more favorable interface is formed and then the viscous bubble could be injected.

Control of the sweep is accomplished by the relative viscosities of the high viscosity bubble and the formation fluids to be displaced, the location of the bubble by the placement of the intermediate (inner offset) injection well, the size of the bubble, the shape of the bubble, and by the time of placement of the viscous bubble.

Any of a number of high viscosity fluids can be used to create the viscous bubble, the primary consideration being that the fluid, after being emplaced, have a higher viscosity than the formation hydrocarbons which are to be swept, yet having a viscosity low enough to permit injection into the formation under reasonable circumstances. Some examples of this viscous fluid would be water thickened with polymers to achieve the desired viscosity, hydrocarbons or crudes more viscous than the hydrocarbons in place in the formation, or any other fluids, such as molasses, which may be ofthe desired viscosity.

when the viscosity of the viscous bubble is not too much greater than the viscosity of the formation hydrocarbons, the viscous bubble moves toward the injection well and with proper combination of relative viscosities, size and placement of the bubble, the viscous .fluid bubble can be moved to the production well and produced before, or shortly after, breakthrough of the driving fluid. This would be desirable in the case that a viscous hydrocarbon were used for the bubble.

Other objects, advantages and features of this invention will become apparent from a consideration of the specification with reference to the FIGS. of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 discloses four units of an inverted five-spot pattern;

FIG. 1a is illustrative of the interface advance in the form of a cusp toward a corner production well in one quadrant of such a five-spot pattern undergoing secondary recovery;

FIG. 2 discloses one unit of a 9-well diagonal pattern;

FIG. 20, corresponding to FIG. la, illustrates the effect of a viscous bubble as it blocks and retards the formation of the cusp at the interface in its advance toward a corner production well in one quadrant ofa 9-well diagonal pattern undergoing secondary recovery;

FIGS. 3a and 3b, illustrate in one quadrant of a 9-well diagonal pattern, the effect of using viscosity ratios which will ermit the viscous bubble to migrate to the corner production well during a secondary recovery program;

FIGS. 4a, 4b and 4c and FIGS. 5a, 5b and 5c illustrate the changes in well functions in accordance with the movement of the interface during the several phases of the production program in a 13-well pattern undergoing secondary recovery;

FIGS. 60, 6b and 6c correspond to FIGS. 4a, 4b and 4c during the production phases applied to a 17-well pattern undergoing secondary recovery; and

FIGS. 6a, 6e and 6f illustrate other changes in well functions in accordance with the movement of the interface during other phases of a program as applied to a 17-well pattern undergoing secondary recovery.

The objects of the invention are achieved by the use of a viscous barrier to retard the formation of the usual cusp interface between the formation and injected fluids in its advance toward a production well of a selected well arrangement by the injection of a fluid more viscous than the formation hydrocarbons to form the barrier.

The specification and FIGS. of the drawings schematically disclose and illustrate the'practice and the advantages of the invention with well patterns and zonal sweep examples which are obtainable and have been observed both in secondary recovery operations and in potentiometric model studies which simulate secondary recovery operations. The model studies indicate a sweep obtained in an ideal reservoir, although the recovery from an actual sweep of a particular field may be greater or less, depending on field parameters.

Throughout the FIGS. of the drawings, the same symbols will be maintained as follows: P and P, represent respectively production wells at the corners and along the sides; I, and I, represent respectively the interior control wells and the central injection well of the arrangement; and, a solid circle indicates a production well,.a crossed circle indicates a shut-in well, an upwardly arrowed open circle indicates an injection well, a downwardly arrowed open circle indicates a converted injection well, and an open circle, a well site. Also, clear areas are swept areas, right diagonal sectioned areas indicate unswept in place formation fluids, and left diagonal sectioned areas, the location of the highly viscous bubble. The diagonal x-x represents an axis of a production well and a pair of offset wells including an injection well.

Referring to FIG. 1, there is disclosed four units of an inverted five-spot pattern wherein the corner wells of each pattern unit are production wells, while the inner central well is used for injection.

FIG. la illustrates the growth of the cusp in one quadrant of an inverted five-spot pattern unit, wherein the secondary flooding fluid is injected into the central well and production is maintained at the corner wells until breakthrough to result in a sweep of approximately 7! percent.

Referring to FIG. 2, there is disclosed a 9-well diagonal pattern, essentially the five-spot pattern with interior injection control wells positioned on the diagonals between the central injection well and the corner production wells.

FIG. 2a illustrates the improvement over prior art. The formation of a cusp is retarded or blocked by the placement in the formation of a viscous bubble via an interior injection control well, I,, After bubble placement, this well is closed in and injection is started or continued at the central injection well, 1,. In this FIG., the interior injection well, 1,, is located midway between the central injection well and the corner production well, P Using a volume of viscous fluid of about 13 percent of a quadrant of a pattern unit volume to form the bubble, the sweep of the formation fluids has been increased by 15 percent over the sweep in a conventional inverted five-spot pattern as illustrated in FIG. Ia, for a total sweep of 86 percent. Another advantage of this invention is that sweeps can be obtained without any production of injected fluids.

In FIG. 3a, the location of the interface of the driving fluid at the time ofthe injection ofthe highly viscous bubble via the interior injection well I, is indicated by the dashed quadrant line, the original location of the bubble being indicated by the sectioned area within the dashed line. At a later stage in the migration of this bubble, the clear area in full outline is the swept area and the sectioned areas show the location of the bubble and the unswept area.

In FIG. 3b, the bubble has migrated to and has been produced to a large extent via the corner production well P while the unswept area has been reduced further, indicating a more complete sweep than in FIG. 2a.

FIG. 4a discloses the basic inverted nine-spot pattern modified by the addition of four intermediate or interior control wells, which can be positioned on the diagonals of the pattern for best advantage as indicated previously. It can be visualized also as a four-unit five-spot pattern, wherein the injection wells of the inverted five-spot pattern units are used for the injection of the viscous fluid, and the innermost production well of the four-unit five-spot pattern has been converted into an injection well for the driving fluid. With such a conversion, the positions of the intermediate wells have been predetermined and may not be situated for best effect.

The first phase of the method of production illustrated in FIGS. 4a and 412 requires that injection of the driving fluid be initiated at the central (or first) well while production is maintained at the second (or intermediate) control wells, I,, with respect to the third (or corner) wells P,. of the quadrilateral pattern. At a predetermined time, e.g. either at breakthrough of the driving fluid or shortly before that, as disclosed in FIG. 4a, the second wells are converted to injection wells for an extraneous fluid, as disclosed in FIG. 4b, usually a fluid having a viscosity greater than that of the driving fluid, which is injected at the central well, or the formation fluids, to form a barrier, as disclosed in my above cited copending application 'for patent, and thereupon production is initiated (or maintained) at the side wells P, of the pattern for a predetermined period, also, either before breakthrough or shortly thereafter. Thereupon, the side wells are converted to injection wells while the second wells are closed in and the first (or central) well of the pattern maintains its injection function. The injection at the side wells may involve either the injection of a highly viscous fluid with a viscosity equal to or less than that injected into the interior control wells 1, or may be the same as the driving fluid injected through the central well I Preferably, while injection through the side wells P, of the highly viscous fluid as illustrated in FIG. 40, is continued for a predetermined period, production is maintained at the corner wells F of the pattern, although if driving fluid, as provided through the central well, is used, then production at the corner wells P is maintained until breakthrough thereof.

Alternatively, as disclosed in FIG. 5a, the first phase of the production method requires injecting a highly viscous fluid via the four interior control wells 1,, and production initiated and maintained at the side wells of the pattern until viscous bubbles of the desired size are produced at the four interior control wells, at which time, these control wells are shut in and injection of the driving fluid is initiated or maintained at the central injection well, with production from the corner wells P,., and the side wells P, for a predetermined period, whereupon the side wells are converted to injection wells. As illustrated in FIG. 5b, a highly viscous fluid is injected to provide blocking bubbles before the corner wells P or as indicated in FIG. 5c, the four side wells are used to inject the driving fluid provided through the central well and production is continued at the corner production wells P until breakthrough occurs.

FIG. 6a discloses a l7-spot pattern which is formed by drilling a single injection wellin a center ofa 4 x 4 well square and converting the four surrounding wells to control wells. In this 17-spot pattern, there are four corner wells, two side wells on each side of the 4 x 4 well square, and four interior control wells located on the diagonals of the pattern and positioned between the central injection well and the corner wells.

Referring now to FIGS. 60, 6b and 60, there are illustrated three steps or phases of a production method as applied to the 17-spot pattern. In the first phase, illustrated in FIG. 6a, with injection maintained at the central injection well, production is maintained at the interior control wells I until breakthrough of the driving fluid or shortly before thereat, thereupon, injection of viscous bubbles is initiated at the four interior control wells, As illustrated in FIG. 612, until the desired size blocking bubbles are achieved at the interior control wells. In the next phase, as illustrated in FIG. 6c, while production is maintained at the side and corner production wells, the four interior control wells are shut in and injection maintained at center well until breakthrough occurs at the side wells. Thereupon, the side wells P, are converted to injection wells, as disclosed in FIGS. 6d and 62, while injection of the driving fluid is continued at the central well. As disclosed in FIG. 6d, a highly viscous fluid is injected via the side wells P, to provide a blocking bubble, the viscosity of this viscous fluid being P, at least equal to that of the driving fluid, and after a predetermined size of bubble has been achieved, production via the corner production wells I,v is either initiated and continued, or maintained.

In FIG. 62, there is disclosed the provision of the same driving fluid as used via the central injection well, for a predetermined time with production via the corner wells P, of the pattern.

In FIG. 6f, there is disclosed the shutting in not only of the four interior control wells, but also the side wells of the pattern, whether formerly used for injection of a highly viscous fluid or the driving fluid, with production at the corner wells P until breakthrough thereat.

It is obvious that this invention can be used to advantage with any pattern which has a well located in a position to place the viscous bubble to obstruct the cusping effect of an interface moving from an injection well to a production well.

Using either of the patterns in FIGS. 4a or a, or 6a, it is possible to shape the bubble by injecting the viscous fluid at the I,- wells and producing only from the P, wells. The viscous bubble will assume an elongated shape in the directions of the nearest production wells. When a bubble of sufficient size and desired shape has been formed, the I, wells will be shut in and injection of normal driving fluid started at the central injection well with production from all of the I, and P wells. Other combinations of production and injection wells can be used to obtain the desired bubble shape.

Any pattern, rate distribution, or other procedure such as placement of a viscous bubble, which retards the development, or the advance, of a cusp towards the production wells will increase the sweep of a field. Two principal means of doing this have been cited above, via: (a) pinning down the cusp by locating production wells between the injection source and the outer production wells, and keeping such inner (or control) wells on production after breakthrough; and (b) spreading the cusp by pulling the front toward side wells until breakthrough the'reat before allowing it to proceed toward the corner production wells of a pattern unit.

Herein has been disclosed still another method of delaying the advance of the interface in the form of a cusp toward an outer production well by injection via a control well and side well of a slug of more viscous fluid than the reservoir fluids to serve as a static block.

Although emphasis has been placed in this disclosure on the practice of this invention as directed to a secondary recovery operation, particularly employing water or other similar aq ucous fluid as the injection displacement fluid, the advantages obtainable in the practice of this invention are also realized in primary hydrocarbon production operations wherein the hydrocarbon-bearing formation is under the influence of either a water or gas drive, or both a water and a gas drive, and also in the instance ofa secondary recovery operation wherein a gas, such as natural gas, is employed as the injection fluid. Moreover, the invention is applicable particularly to an arrangement of a pair of wells in line with an injection well under the influence of an active water drive.

Iclaim:

I. A method of producing formation fluids including hydrocarbons from an underground hydrocarbon-bearing formation which comprises penetrating said formation with at least three wells, a first well, a second well and a third well, said wells being substantially in line and the second and third wells being on one side of said first well, said three wells in line being part of a quadrilateral well pattern wherein the central well of said pattern is said first well and the remaining pattern wells are arranged along the sides and on the diagonals of said pattern equally therealong, injecting an extraneous driving fluid into said formation via said first well to displace fluids including hydrocarbons in said formation toward the second and third wells, producing said formation fluids including hydrocarbons from said formation via said second wells, ceasing producing said formation fluids and then injecting into said formation via said second wells a highly viscous fluid having a viscosity greater than that of the formation and driving fluids, and initiating and for a predetermined time period producing said formation fluids including hydrocarbons from said formation via the side wells of said pattern while injecting extraneous fluid into said formation via said first well, thereupon injecting into said side wells a fluid having a viscosity equal to or less than said fluid injected via said second wells and producing from the corner wells of said pattern,

2. In a method as defined in claim I, injecting said highly viscous fluid into said formation via said second wells prior to breakthrough of said extraneous fluid thereinto.

3. In a method as defined in claim 1, injecting said highly viscous fluid into said formation via said second wells upon breakthrough of said extraneous fluid thereinto.

4. In a method as defined in claim 1, said injecting of said highly viscous fluid via said second wells being of a predetermined percentage of the pattern unit volume, to provide a static barrier between said first and third wells.

5. In a method as defined in claim 4, the highly viscous fluid comprising formation hydrocarbon fluids treated with thickeners to increase the viscosity thereof prior to injecting thereof into said formation via said second wells.

6. In a method of producing formation fluids as defined in claim 1, the injecting of said extraneous fluid into said formation via said first well continuing until breakthrough thereof at said side wells.

7. In a method of producing formation fluids as defined in claim I, concurrently initiating and maintaining producing said formation fluids from said second and side wells.

8. In a method of producing formation fluids as defined in claim I, producing formation fluids from said third wells while injecting a predetermined amount of the viscous fluid into said formation via said side wells.

9. in a method of producing formation fluids as defined in claim 1, said three wells in line being part of a 13-well well diagonal pattern.

10. in a method as defined in claim 9, said second wells being spaced away from said first wells by at least three quarters of each distance between said first well and said third wells.

11. ln a method of producing formation fluids as defined in claim 1, simultaneously initiating producing said formation fluids via all of said wells along said sides and said diagonals of said quadrilateral.

12 in a method of producing formation fluids as defined in claim 11, producing formation fluids via said wells located on the diagonals of said pattern adjacent said injection well and continuing'producing therefrom until breakthrough of said extraneous fluid occurs, thereupon converting said aforementioned diagonal wells into injection wells and injecting into said formation via such converted wells the driving fluid, and initiating and continuing producing from the side wells of said pattern until extraneous fluid breakthrough occurs thereat, thereupon initiating and maintaining producing said formation fluids via the corner wells of said pattern until extraneous fluid breakthrough occurs thereat.

l3. In a method of producing fluids as defined in claim 1, said three wells in line being part of a 17-well pattern, the central well being an injection well and the remaining wells being located in equal numbers along the sides and on the diagonals of a quadrilateral.

M. A method of producing formation fluids including hydrocarbons from an underground hydrocarbon-bearing for- 8 mation which comprises penetrating said formation with at least three wells substantially in line, a first well, a second well and a third well, the second and third wells being on one side of said first well, said-three wells in line being part of a quadrilateral well pattern wherein the central well of said pattern is said first well and the remaining pattern wells are arranged along the sides and on the diagonals of said pattern equally therealong, injecting a driving fluid into said formation via said first well to displace fluids including hydrocarbons in said formation toward said second and third wells while injecting into said formation via the second wells, a highly viscous fluid having a viscosity greater than that of the formation and driving fluids for a predetermined time period, and thereupon initiating and producing for a predetermined time period fluids including hydrocarbons from said formation via the side wells and thereafter injecting extraneous fluid into said formation via said side wells and producing from said corner wells of said pattern.

15. in a method of producing formation fluids as defined in claim 14, said injecting of said highly viscous fluid via said second well being of a predetermined amount of a percentage of the pattern unit volume.

16. In a method as defined in claim 14 said extraneous fluid having a viscosity equal to or less than that of said highly viscous fluid.

17. in a method as defined in claim 14, said extraneous fluid being said driving fluid.

18. In a method as'defined in claim 14, said extraneous fluid being said highly viscous fluid. 

